The present invention relates to an electrical circuit and particularly to an electrical circuit for alternately actuating a pair of loads with an initially high actuating current followed by a lower holding current.
In industries such as the label printing industry, it is desired to rapidly stepwise advance a web of label material through a printing press or a label cutting machine. In order to advance the web at a speed sufficiently rapid to provide a large volume output of relatively small labels it can be appreciated that the web material must move rapidly into, for example, printing stations or label cutting stations. Naturally, the web feeding mechanism must position the web accurately for successive printing and/or cutting operations. Thus, for example, for printing an accuracy of 0.005 of an inch registration is required particularly where multi-colored printing is being employed.
In the past, a variety of feed mechanisms have been employed for feeding, for example, labels through a label cutting machine. Rollers which selectively advance the web stock label material have been employed and include a moveable idler roller to alternately compress the stock between a driven roller and the idler roller and release it for advancing and stopping the web, respectively. With such prior art, however, where complex mechanical linkages are used, only approximately 300 labels per minute can be run through the device. Representative of such prior art machines is the present assignee's Model No. CF-180.
In order to significantly increase the speed of operation of such machines, it has been discovered that electrical drive of the pinch roller directly on a slide and/or clamping mechanism for holding the web stock in position is desired. Operation of electrically driven solenoids, however, is relatively slow unless such solenoids are actuated with an initial high current impulse followed by a lower holding current. The concept of providing this type of actuation for solenoids is well known as are some types of electrical circuits to provide such operation. Representative of such prior art are U.S. Pat. Nos. 3,599,804, issued Aug. 17, 1971 to P. O. Chorney; 3,248,633, issued Apr. 26, 1966 to J. J. Guarrera; 4,001,664, issued Jan. 4, 1977 to T. M. Hyltin; and 3,411,045, issued Nov. 12, 1968 to N. L. Reyner.
It has also been discovered that in order to speed up the operation of label printing and cutting machines, it is desirable not only to electrically direct drive the means for advancing the web stock through the machine, but also electrically drive clamping mechanism for stopping and holding the web stock in registration. The drive means and the clamping means are alternately operated for the stepwise advancement of the web stock material.